Some believe that the executive should control foreign policy, others that the legislature should do so. But whatever view one takes of the theory, one thing is certain about the practice: an administration that can't shape its foreign policy risks being seen abroad as weak. This is precisely where the Government stands today. Yesterday morning, it was poised to move a Commons motion proposing immediate military action against the Assad regime. A day later, it is proposing one suggesting such action later…perhaps…after the report of the U.N Investigation Team…despite that team having no mandate to "apportion blame" (in the words of the motion)…and after further efforts to secure a Security Council resolution…despite previous efforts to do so having been unsuccessful because of the council's "failure…to take united action" (again in the words of the motion). These contortions and contradictions only highlight what is not so much a U-turn as a V-turn.

It isn't yet clear whether Ed Miliband took a lead, and went for Cameron's throat in the same way that he eventually went for Rupert Murdoch's over Leveson, or whether he merely followed his own Iraq-traumatised backbenchers' reluctance to support the Government. Similarly, it also isn't apparent whether the Prime Minister took the initiative in amending his own motion, or whether others in government confronted him with the brutal reality – namely, that he was set to lose this evening's vote. Hence the climbdown. The simple fact is that Cameron began the week by talking very big about Syria, and will end it by acting very small. In one sense, this is arguably for the good. It isn't clear why a missile strike on a few Syrian military compounds or Presidential palaces would deter the Assad regime from using chemical weapons again, assuming (as it is reasonable to do) that it used them recently in Damascus. And as I have written many times on this site, Britain must not be drawn into Syria's civil war.

But in another sense the Prime Minister's self-defenestration is very bad indeed – bad for him and bad for Britain. North Korean despots, Iranian ayatollahs, Taliban warlords, Russian strongmen and Chinese spooks may not spend their spare evenings poring over Hansard. But they follow what happens in Britain more closely than many imagine. Cameron may not have been right to want to strike speedily at Assad. None the less, Prime Ministers have responsibilities that war-weary voters and publicity-friendly backbenchers do not. It is far from impossible to imagine Cameron wanting to act swiftly and rightly in a crisis, and being blocked by an opportunist official opposition and diehard internal opponents. That, at any rate, will be how some of Britain's enemies read yesterday's events. President Obama may have to act without the support of an ally on which he was relying. It would be an exaggeration to write that Britain cuts a diminished figure in the world this morning. But maybe not by all that much.

To all of which, the Prime Minister would be entitled to reply: "So what would you have done, then, in my position?" It's a fair question: writing as a critic is easy; acting as a leader is hard. But maybe the best answer is all to do with the triple obstacles to a missile strike I wrote about earlier this week – the Cabinet, Conservative backbenchers and the opposition. Cameron could perhaps not have foreseen Miliband's finesse in relation to the UN inspectors, though some will say otherwise. But the fact is that the recent Tory poll recovery has swung Party morale in some quarters from near one of its polarities (despair) to near another (hubris). Rosier economic prospects, the Labour leader's dire summer and CCHQ's new attacking zest have lulled some in Number 10 into a false sense of security. Certainly, both the Cabinet and backbenchers appear to have been taken for granted during this week's preparations for today's vote – when it was very clear that neither are enthused by a strike on Syria.

One Cabinet Minister claimed to me yesterday that the first he heard about the Government's retreat was from his TV. And either the Whips failed to grasp the scale of any potential revolt, or weren't consulted or listened to (not for the first time). The Prime Minister will need to renew his charm offensive to backbenchers after calling them back to the Commons for nothing: an overture that began in earnest, it should be noted, after another Downing Street mess-up, over John Baron's amendment to the Queen's Speech. All in all, what has driven the screech of brakes over Syria is the old familiar truth – namely, that Cameron doesn't have full control of the car. He has no Commons majority. He is dependent on the Liberal Democrats and truculent backbenchers. That means reaching for two remedies that this site has suggested before – using senior Cabinet members and '22 officers more extensively and his Whips Office more acutely. Especially when the Government's standing among its peers abroad is at stake.